[3.1.190618-rc1] - History Cointracking Export

**Describe the bug**
Number of commas is changing during iteration

**To Reproduce**
Steps to reproduce the behavior:
1. History Export -> Elasticsearch
2. Cointracking.info
3. Open file with text reader
4. See error

**Expected behavior**
only one comma

**Screenshots**
```
Withdrawal,,,0.02526,BTS,,,BTS-DEX,,limit_order_create fee,08.06.2019 04:31:48 GMT+0200
Trade,241.86786,BTS,1460.266,RUDEX.SMOKE,,BTS,BTS-DEX,,,08.06.2019 04:31:48 GMT+0200
```

**Desktop (please complete the following information):**
- OS: MX-Linux. Light client

Start with the History Export → Elasticsearch → Cointracking.info flow and inspect how the export rows are assembled. Reproduce the shown rows in a text reader, then verify that iteration no longer adds extra commas and that each field remains correctly separated.

Written by the indexing model from the issue text.